1. Field of the Invention
This invention relates to an electrostatic chucking method used for fabricating a semiconductor device, and more particularly to an electrostatic chucking method capable of eliminating residual electric charges that accumulate on a chucking material (or an insulator) in an electrostatic chucking apparatus.
2. Description of the Prior Art
FIG. 1 shows mainly a cross-sectional view of an insulator used as a chucking material in an electrostatic chucking apparatus used for a conventional method of electrostatic chucking. In FIG. 1, the numeral 21 designates an electrostatic electrode which comprises a thin copper plate, and 22 denotes the insulator. The electrode 21 is embedded in the insulator 22. On the insulator 22 is placed a material such as a semiconductor substrate 23 to be chucked electrostatically by the electrostatic chucking apparatus.
The numeral 24 designates a direct current power source, 26 and 25 refer to a positive electrode and a ground negative electrode, respectively. The numeral 27 denotes a switch for switching either a positive potential or a ground potential through the electrostatic electrode.
In the electrostatic chucking apparatus having the construction described above, the switch 27 is connected to the positive electrode 26 to electrostatically chuck the semiconductor substrate 23 to the insulator 22. Thereafter, since the electrode 21 is kept at a positive potential, the semiconductor substrate 23 is chucked electrostatically so as to be firmly fixed to the insulator 22.
After a predetermined process has been carried out, when the semiconductor substrate is removed from the insulator 22, the switch 27 is switched to the grounded negative electrode 25. This enables the semiconductor substrate 23 to be removed from the insulator 22, thus completing the electrostatic chucking process.
However, there is a problem in the conventional electrostatic chucking method described above. Namely, charges on the semiconductor substrate 23 become transferred to the insulator 22 after each electrostatic chucking process, which thereby increases the amount of residual charges on the insulator 22. Consequently, when the amount of residual charges on the insulator 22 increases, the electrostatic chucking force of the insulator 22 decreases. This means that the semiconductor substrate 23 will be held to the insulator 22 by a force that gradually gets weaker and weaker.
It should be noted that in the explanation described above, the electrostatic electrode 21 is supplied with the positive potential by the direct current power source 24.
FIG. 2 shows a cross-sectional view of an insulator used as a chucking material in another conventional electrostatic chucking apparatus used for a conventional method of electrostatic chucking. In FIG. 2, two electrodes 32 and 33 are embedded in an insulator 31. The numerals 37 and 38 designate switches and 34 designates a direct current power source. The numerals 35 and 36 refer to a positive electrode and a negative electrode, respectively.
The problem mentioned hereinabove also occurs in the electrostatic chucking apparatus of FIG. 2. Namely, the residual charges are increased on the insulator 31 when the electrode 32 is supplied with a positive potential and the electrode 33 with a negative potential.
For both types of conventional electrostatic chucking apparatuses described above, this problem in the prior art cannot be resolved.